A wireless sensor network (WSN) is an example of a network in which multiple devices (i.e., nodes) communicate with each other using a specific communication protocol. Among the communication protocols for WSNs, medium access control (MAC) is a technique that enables nodes to operate in a shared-medium network. For any MAC protocol design, there are three operational parameters that are taken into consideration: (1) collision avoidance with other nodes transmitting simultaneously on the same medium, (2) prevention of overhearing of signals at neighbor nodes that are not the intended target of a signal, and (3) efficient utilization of energy. There are a variety of protocols that have been developed for data communication networks, such as time-division multiple access (TDMA), code-division multiple access (CDMA), and contention-based protocols like IEEE 802.11. The third parameter (i.e., efficient energy utilization) becomes important in the context of WSNs because the devices are typically small, powered by tiny batteries, and not amenable for regular maintenance. Therefore, it is desirable to find an energy efficient data representation and communication protocol.
MAC protocol design for wireless sensor networks is a broad research area and can be divided into TDMA-based protocols, contention-based protocols, and hybrid protocols. Pulse-based methods are also used in protocol design of WSNs and other applications to achieve energy efficiency, security, and cooperation between heterogeneous wireless devices.
In TDMA-based protocols, a duty cycle is built in to preserve energy and such protocols typically do not suffer from collision. However, TDMA-based protocols are not widely accepted due to their high complexity and overhead due to non-trivial problems of synchronization. Furthermore, TDMA-based protocols may not support node-change scalability and it is difficult to manage inter-cluster communication.
Among contention-based protocols, S-MAC is a well-known protocol that uses a fixed listen/sleep cycle to conserve energy. S-MAC significantly reduces energy consumption by periodically putting nodes into sleeping mode. Another contention-based protocol that is based on S-MAC is a T-MAC protocol in which the fixed listen/sleep cycle of S-MAC is provided as adaptive sleep/active duty cycle for radio operation. There have also been other protocols proposed in recent decades which are based on this listen/sleep cycle, like ADV-MAC and R-MAC. Some hybrid protocols, like Z-MAC, have the properties of both TDMA and Carrier Sense Multiple Access (CSMA). The protocols are based on traditional packet transmission, which suffers from the overhead of large numbers of bits within a data packet, header, and preambles. The transmission of such overheads can be prohibitively energy-inefficient.
Pulse communication has been applied in the research of WSNs for several years, due to the pulse modulation advantage on energy saving during transmission. A power-efficient communication model, which uses pulse and silence, is proposed for computing a function of data in a wireless sensor network. However, the pulse communication is restricted to communication between sensor nodes and base stations (satellites), and does not involve transmission of information between neighbor sensor nodes.
Data encoding based on pulse width and pulse position also has broad applications in engineering. TDMA-like pulse encoding principles increase data transmission rates based on commercial grade LEDs and LRDs. Other pulse encoding methods based on pulse position modulation have also been developed to target the error correction or bit distinguishing. However, the basic data expression is still binary and pays for the overheads of headers and preambles within the traditional packet transmission. Although the above MAC protocols can improve the idling energy expenditure in low duty-cycle networks, they still use traditional binary encoding principles and suffer from packet overheads.